This application is based upon and claims benefit of priority of Japanese Patent Applications No. 2001-189798 filed on Jun. 22, 2001 and No. 2002-70434 filed on Mar. 14, 2002, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an engine-starting apparatus which is used in a system for automatically stopping an internal combustion engine of an automotive vehicle under predetermined conditions and for re-starting the engine under other predetermined conditions.
2. Description of Related Art
A system (so-called engine-idle stop system), which automatically stops an engine under certain conditions, e.g., when a vehicle temporarily stops at an intersection, and automatically re-starts the engine under predetermined conditions, e.g., when the vehicle is driven again, has been known hitherto. This system contributes to reduction of fuel consumption and reduction of exhaust gas pollution. A starter motor having a jump-in pinion is used in this system, for example. However, this type of starter motor is not able to re-start the engine while the engine is still rotating before it comes to a complete stop. Accordingly, the engine has to be re-started after it comes to a complete stop, resulting in a slow response in re-starting operation. Further, noises caused by re-starting the engine is uncomfortable.
In order to re-start the engine while it is still rotating by its inertia, it is proposed to connect the starter motor via a belt. For example, JP-A-9-172753 proposes a starter motor connected to a crankshaft of an engine via a belt. This starter motor includes an overrunning clutch that prevents the starter motor from being driven by the engine after the engine is cranked up. The overrunning clutch disconnects the starter motor from the engine when the engine reaches a rotational speed exceeding a predetermined speed. However, there is a problem as described below in this system.
When the engine stalls for some reasons after it is once cranked up, the engine speed temporarily increases and then it comes to a rapid stop. At a time when the engine speed temporarily increases, the starter motor is disconnected from the engine by operation of the overrunning clutch, and thereby the rotational speed of the starter motor increases to a speed close to its no-load speed by its inertia. Then, the rotational speed of the starter motor decreases more gradually than the engine speed. This means that the engine speed is higher than the starter motor speed at the beginning, and then the starter motor speed exceeds the engine speed. If the overrunning clutch is engaged at this moment, an engagement shock and noises are generated due to a speed difference between the engine and the starter motor. This may results in breakdown of the overrunning clutch.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide such a starting apparatus for use in the so-called engine-idle stop system that is able to smoothly re-start an engine when the engine is still rotating by its inertia while avoiding troubles in re-engagement of an overrunning clutch.
The engine-starting apparatus of the present invention is composed of an electric motor and an overrunning clutch for transmitting the rotational torque of the electric motor to the internal combustion engine and for intercepting torque transmission from the internal combustion engine to the electric motor. The overrunning clutch is composed of a driving member connected to the electric motor, a driven member connected to the internal combustion engine and a coupling member disposed between the driving member and the driven member for coupling and separating the driving member to and from the driven member.
A separating speed of the driving member at which the driving member is separated from the driven member is set to a point where the rotational speed of the driven member exceeds the rotational speed of the driving member. A coupling speed of the driven member at which the driven member is re-coupled to the driving member is set to a predetermined point. The electric motor is switched off at the separating speed and switched on again when the rotational speed of the driven member becomes equal to or lower than the coupling speed.
The coupling speed of the driven member is set to a speed equal to or a little higher than a level where the driven member speed becomes equal to the driving member speed under a situation where the internal combustion engine stalls after it is once cranked and the engine speed decreases more quickly than that of the electric motor. Alternatively, the coupling speed is set to a speed equal to or a little higher than a maximum no-load speed of the electric motor. Preferably, the coupling speed is set to a speed lower than the separating speed to avoid repetition of separating and re-coupling operation of the overrunning clutch. Either the separating speed or the coupling speed, or both may be set to a speed lower than a level at which a film for lubricating the coupling member is disconnected.
By switching on the electric motor again when the driven member speed decreases to the coupling speed or lower, shocks and noises otherwise generated at the re-coupling of the overrunning clutch can be avoided, and the internal combustion engine can be smoothly re-started while it is still rotating by its inertia. More particularly, under a situation where the engine stalls after it is once cranked, the engine can be smoothly re-cranked while it is still rotating by the inertia. Under a situation where the engine is automatically stopped at an intersection, it can be smoothly re-cranked without waiting until it comes to a complete stop. A time required for re-cranking the engine is shortened and the re-coupling shocks and damages to the clutch are avoided at the same time.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.